Harmful algal bloom

A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, mechanical damage to other organisms, or by other means. HABs can cause significant harm to animals, the environment and economies. They have been increasing in size and frequency worldwide, a fact that many experts attribute to global climate change.

HABs are induced by eutrophication, which is an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (nitrates, ammonia, and urea) and phosphate. The excess nutrients are emitted by agriculture, industrial pollution, excessive fertilizer use in urban/suburban areas, and associated urban runoff. Higher water temperature and low circulation also contribute.

When these blooms die, the microbes that decompose the dead algae use up more of the oxygen, generating a "dead zone" which can cause fish die-offs. These events can happen naturally, but human activities, such as fertilizer use and pollution, often make them worse. The U.S. National Oceanic and Atmospheric Administration (NOAA) predicts more harmful blooms in the Pacific Ocean.

Description and identification

Harmful algal blooms (HABs) from cyanobacteria, also known as blue-green algae, can look like foam, scum, or a mat on the surface of water. They may be bright green or other colors depending on their pigments. These blooms are a problem all over the world, especially in warm waters that have too many nutrients.

These blooms can be harmful because they make toxins or use up oxygen in the water. This can hurt fish and other animals. Not all algal blooms are harmful — some only change the color or smell of the water. To know if a bloom is harmful, scientists need to take samples and study them under a microscope or use special tools to detect toxins.

Terminology

Harmful algal blooms, often called "red tides" in coastal areas, are large groups of algae that can harm other living things. In a narrow sense, these blooms are harmful mainly because they release toxins that affect other species. However, any algal bloom can create "dead zones" where there is too little oxygen for sea creatures to survive, which can also be considered harmful.

The term "red tide" comes from blooms of certain dinoflagellates, like Karenia brevis, but this name can be confusing. Algal blooms can be many colors, and their growth is not related to the tides. Not all red tides are caused by dinoflagellates; some are created by other tiny organisms. Scientists are now using more precise terms like "harmful algal bloom" for harmful species and "algal bloom" for those that are not harmful.

Main article: Red tide
Main articles: Algal bloom, Algal bloom#Harmful_algal_bloom

Types

There are three main types of tiny floating organisms that can form harmful algal blooms: cyanobacteria, dinoflagellates, and diatoms. These organisms can make their own food from sunlight through photosynthesis, which makes them important for small fish and other sea creatures.

Cyanobacteria, often called blue-green algae, can produce toxins that harm the liver and nervous system. They can also block sunlight and lower oxygen levels in water, which can harm fish and other animals. Diatoms and dinoflagellates are mainly found in ocean areas and can also form harmful blooms, sometimes helped by human activities. Some of these algae produce toxins that can hurt animals and people if they eat affected seafood.

Causes

Sometimes it is unclear what causes specific harmful algal blooms (HABs), as their occurrence in some places seems natural, while in others it results from human activities. Many different algae species can form HABs, each needing different conditions to grow well. In some areas, HABs happen more often and become worse because of extra nutrients from human activities. In other places, HABs are a regular seasonal event due to natural ocean currents.

The growth of algae is usually limited by the amount of nitrates and phosphates available, which can be plentiful in coastal areas and from agricultural runoff. The type of these nutrients also matters, as different algae grow at different rates depending on what is available. Other factors like iron, silica, and carbon can also affect algal blooms. Human-caused factors such as water pollution and rising sea water temperature may also contribute to HABs.

Nutrients

Further information: Eutrophication

Nutrients get into water from agricultural pollution, urban runoff, and sewage treatment plants that lack proper nutrient control. Coastal areas, especially places like the Mediterranean Sea, often receive untreated sewage, which adds more nutrients to the water. These extra nutrients can lead to more frequent and severe HABs.

Iron fertilization

Main article: Iron fertilization

Adding iron to ocean areas that lack it can encourage the growth of phytoplankton. This is done to increase plant growth and help remove carbon dioxide (CO₂) from the air. Iron is important for plants to make food through photosynthesis.

Climate change

Further information: Effects of climate change on oceans

Climate change leads to warmer waters, which create better conditions for algae to grow in more places, including areas farther north. Warmer water and high-nutrient conditions in lakes and rivers increase the chance of HABs. Since the 1980s, HABs seem to be happening more often and in more places, partly because of human activities like adding nutrients to water and the warming of ocean temperatures.

Causes or contributing factors of coastal HABs

HABs often appear as discolored water, sometimes reddish-brown. While they are a natural event, the exact reasons they happen are not always known. Natural factors like salt levels, temperature, and wind can play a role. Human activities, such as water pollution from sewage and agricultural runoff, can also contribute. In some places, HABs occur naturally due to ocean currents, while in others, they result from extra nutrients caused by humans. Factors like dust from deserts and climate patterns such as El Niño can also influence HABs.

Number and sizes

The number of harmful algal blooms has been going up around the world. Scientists are not sure if this is because there are actually more blooms or because we are getting better at spotting and identifying them.

These blooms have been reported in many places, including Europe, Africa, Australia, and India. They have even appeared in surprising locations like the Arctic, Antarctica, and mountain ranges such as the Himalayan Mountains, the Rocky Mountains, and the Sierra Nevada Mountains. In the United States, every coastal state has dealt with harmful algal blooms in recent years. Major rivers, like the Ohio River, have also seen big blooms that can stretch for hundreds of miles. Climate change is expected to make these blooms happen more often in the future. Off the coast of South Africa, certain blooms happen every spring and can make shellfish unsafe to eat.

Harmful effects

Further information: Eutrophication § Effects

As algal blooms grow, they use up oxygen in the water and block sunlight from reaching fish and plants. These blooms can last from just a few days to many months. Without enough light, plants under the bloom may die, and fish may starve. At night, the dense algae use oxygen, lowering its levels. When the algae die, tiny organisms that break down the dead algae also use more oxygen, which can cause more fish to die or leave the area.

If oxygen levels keep dropping, it can create areas called dead zones where fish and plants cannot survive. These dead zones can also release methane, a gas that traps heat in the atmosphere. Scientists think that harmful algal blooms played a role in some of Earth’s biggest events where many plants and animals died long ago.

Human health

Some toxins from algal blooms can be breathed in from the air near affected waters, which may affect health. Not all blooms release harmful toxins into the air; it depends on the type of algae and the conditions. Toxins can be carried far by the wind.

Eating fish or shellfish from areas near blooms is not advised because these animals can collect toxins. This can lead to several types of poisoning in humans. In 1987, a new kind of poisoning called amnesic shellfish poisoning was found after people ate mussels from Prince Edward Island. The toxin came from a type of algae in the water where the mussels grew. Other types of poisoning, like paralytic shellfish poisoning, have also caused deaths in places like the Philippines.

After a bloom in Monterey Bay, California, health officials warned people not to eat certain fish like anchovies, sardines, or crab caught there. In 2015, many shellfish fisheries in Washington, Oregon, and California closed because of high levels of toxins in shellfish. Breathing in vapors from waves during a bloom can sometimes cause breathing problems.

In 2018, officials in Utah worried that crops might get contaminated if watered with toxic water, though they said it was hard to measure.

People are usually warned not to drink or even touch water from algal blooms, and pets should stay away too. In 2014, Toledo, Ohio, told its residents not to drink tap water because a bloom in Lake Erie made the water unsafe. Similar issues happened in Kenya, China, and Australia.

Symptoms from drinking toxic water can include feeling sick, throwing up, or having trouble with digestion. In rare cases, it can be very serious. Touching the water might cause skin rashes or eye irritation.

Economic impact

Algal blooms can harm tourism and recreation. In places like Florida, California, and Utah, people have avoided beaches and lakes because of the risks. This hurts local businesses. Similar issues have happened in Europe, including France.

The fishing industry also suffers. In 1976, a bloom near New York and New Jersey cost fisheries over $500 million. In 2009, a bloom in Hong Kong killed valuable fish worth over $10 million. The U.S. seafood industry worries about losing money each year. In 2015, a huge bloom shut down shellfish fishing on the West Coast for the first time ever.

Environmental impact

Algal blooms can create dead zones where there isn’t enough oxygen for fish and other animals to survive. These dead zones can grow and rarely go away. One dead zone in the Black Sea got better after changes in farming practices.

Blooms can also kill fish directly. In 2016, a bloom in Chile killed 23 million salmon being farmed. Fish die-offs have happened in many places, including Rio de Janeiro, Brazil, and Monterey Bay in the U.S.

Land animals like pets and livestock can also get sick or die from toxins in the water. Marine animals like dolphins, whales, and sea turtles have been harmed or killed by these toxins. Birds that eat contaminated fish have also died.

Harmful algal blooms can hurt many sea animals, including dolphins, sea turtles, seabirds, and fish. The toxins can affect their health in many ways, such as causing problems with their nerves or immune systems. Some animals can even die from eating contaminated fish or shellfish.

Potential remedies

Further information: eutrophication § Reversal and remediation

Many algal blooms happen because too many nutrients, like nitrates and phosphorus from fertilizers, flow into lakes and rivers, especially after heavy rains. To help stop this, scientists suggest better farming methods, such as using drip irrigation, which delivers water and fertilizer directly to plant roots. This reduces the amount of fertilizer that runs off into water. Creating buffer zones with plants and wetlands can also help trap nutrients before they reach the water.

Chemical treatments can kill algae, but they can also harm fish and other wildlife. In some places, new chemicals have been tested and worked well. For example, Chippewa Lake in Ohio cleared its toxic algae in one day using a special treatment. Scientists are also studying natural ways, like using compounds from seaweeds, to control harmful algae without causing harm to the environment. Some methods use special clays that trap algae in the sediment, helping to reduce blooms.

Notable occurrences

Harmful algal blooms, also known as red tides, happen when algae grow too much and can harm fish, plants, and sometimes people. These blooms can happen in many places around the world.

Some important times when harmful algal blooms happened include:

• In 1793, a bloom was first recorded in British Columbia, Canada.
• In 1844, a possible bloom was seen off the Florida Gulf Coast.
• In 1901, bright glowing waters were seen in Southern California because of algae called Lingulodinium polyedrum.
• In 1972, a bloom in New England made shellfish dangerous to eat.
• In 1991, a huge bloom happened in the Darling River in Australia.
• In 2005, a bloom was found further south than usual along the U.S. East Coast.
• In 2008, big algae blooms caused damage in the Chesapeake Bay.
• In 2013, a bloom happened in China near Qingdao.
• In 2014, a bloom in Lake Erie made the water in Toledo, Ohio, unsafe to drink.
• In 2017 and 2018, a serious bloom in Southwest Florida hurt fish, dolphins, and manatees.

Blooms keep happening in many places, like off the coast of Florida, in the Gulf of Mexico, and in lakes such as Lake Erie. These blooms can close beaches, hurt fishing, and sometimes make the water unsafe.